“We ran the DNA to see if we could connect the different crime scenes and 400 different dogs, which we were able to do,” said Dr. Melinda Merck, a forensic veterinarian for the A.S.P.C.A. “A lot of times defendants will claim not only that they are not dog fighting, but also that they’re just breeding and they don’t know each other.”

The DNA showed otherwise, indicating that many of the dogs were related. The July raids have yielded at least 17 guilty pleas, and while the DNA evidence did not conclusively prove a relationship among defendants, it certainly suggested one. Investigators caution, however, that DNA evidence alone will rarely make a case, though many juries have come to expect it.